Mercuric Chloride by Phosphorous Acid. 357 



As a matter of fact the constants calculated from this equation 

 gradually increase.* This, however, may very reasonably be 

 ascribed to the influence of complex molecules of the types 

 H 2 Hg 2 Cl 6 , etc., which are known to form in the presence of 

 hydrochloric acidf and which probably do not react, as 

 such, with the phosphorous acid. Since these complexes break 

 up with increasing dilution, the velocity coefficient as calcu- 

 lated by equation (6) ought to rise, as is actually the case. 



It is a remarkable fact that if in equation (5) (a — x) is 

 replaced by {a — ^x) fairly concordant constants are obtained 

 from all the experiments performed in aqueous hydrochloric 

 acid. This modified equation, although empirical, may be 

 derived from hypothetical considerations as follows : Assum- 

 ing that the complex which mercuric chloride forms with 

 hydrochloric acid in water solution is chiefly H 2 Hg 2 Cl 6 (and this 

 assumption explains the phenomena observed in the cryoscopic 

 and conductivity measurements, which Le Blanc and Noyes 

 ascribe to the formation of the complex H 2 HgCl 4 ) and that 

 the reaction takes place essentially between the phosphorous 

 acid and the single molecules of HHgCl 3 which are formed by 

 the depolymerization of the double molecules H 2 Hg 2 Cl 6 , it fol- 

 lows that the concentration of the molecules HHgCl 3 at any 

 time t is not (a —x) but m{a — x), where m denotes that frac- 

 tion of the total mercuric chloride present, at any time t, 

 which is in the form of single molecules, HHgC] 3 . Equation 

 (5) may then be written: 



— = km(a — x) (b — %x) (C + x), (V) 



(it 



* See Ki in Tables III, IY, Y and YI. 



f According to LeBlanc and Noyes (Zeitschr. phys. Chem., vi, 329) mer- 

 curic chloride in the presence of aqueous hydrochloric acid forms complex 

 compounds, such as HHgCl 3 .H 3 HgCl5, H 2 HgCl 4 , H 2 Hg 2 Cl 6 and others more 

 complex. They also found that the conductivity of normal hydrochloric 

 acid is gradually depressed by 1*7 per cent if the solution is % normal with 

 respect to mercuric chloride, and by 17'9 per cent if the solution is normal 

 with respect to mercuric chloride. This phenomenon they attribute partly to 

 the extremely slow movement of the complexions and partly to their retard- 

 ing effect on the hydrogen ions, and not to a lowering in the degrees of ion- 

 ization of the complex compounds, since when mercuric chloride is mixed 

 with aqueous hydrochloric acid in the proportion of HgCl 2 : HC1 the solution 

 has the same catalytic effect upon the hydrolysis of methyl acetate as when 

 the mercuric chloride is absent. This abnormal decrease in the conduc- 

 tivity may also be due to the fact that the equilibrium in the equation, 



HHgCls + HHgClsT— >H,Hg,Cl B . 



is shifted to the right with the increase in the concentration of the solution 

 with respect to the mercuric chloride, and conversely. For further evi- 

 dence in support of the assumption that the type of complex is (HHgCl 3 )n and 

 not H 2 HgCl 4 , see J. Sand and F. Breest, Zeitschr. phys. Chem., lix, 426 and 

 lx, 237. Also Jander, Zeitschr. Electrochem., viii, 688. 



